I. Field of the Invention
This invention relates generally to implantable medical tissue stimulating devices, and more particularly to a hermetically sealed pulse generator with an independent, hermetically sealed battery compartment.
II. Discussion of the Prior Art
Implantable pacemakers, cardiac defibrillators and neural stimulators typically comprise a single hermetically sealed case or housing containing a microprocessor and a pulse generator controlled by the microprocessor for delivering tissue stimulating pulses at programmed time intervals along with a battery power supply for supplying electrical current to the electronic circuitry. Given the complexity and capabilities of present-day tissue stimulators, they may have a manufacturing cost approaching ranging between $1,000.00 and $3,000.00.
The battery power supply may typically comprise a lithium iodide cell in that such batteries do not generate a gas during discharge that would make the sealing of the implantable device problematic. Implantable medical devices of the type described herein have a somewhat limited shelf life and a substantial cost burden is incurred by the manufacturers of such devices in the event that sales do not deplete the inventory quickly enough. In that the battery and the somewhat expensive electronics are necessarily contained within a hermetically sealed container or housing, the entire device must be scrapped if the unit is not implanted within a period of 12 months of manufacture for certain modules and 24 months for others. Taking into account the number of different models of pacemakers and AICDs manufacturers produce and the need to maintain an inventory of each, losses due to scrapping can easily reach several million dollars per year due to battery depletion.
During the test and burn-in phase of manufacture, the implantable device is subjected to elevated temperatures to stress the integrated circuits and other components of the microprocessor-controlled pulse generator to detect hardware faults. The elevated temperatures are known to cause battery degradation.
Thus, a need exists for an implantable tissue stimulator that will have a fresh, fully charged battery at the time of implant irrespective of the date of manufacture. The present invention provides a solution.